The SLS reuses liquid hydrogen engines and solid rocket boosters from Shuttle by law, which has made it antiquated, massively expensive and paradoxically five years late.

“ In 2011, Rep. Tom McClintock and other groups called on the Government Accountability Office (GAO) to investigate possible violations of the Competition in Contracting Act (CICA), arguing that Congressional mandates forcing NASA to use Space Shuttle components for SLS are de facto non-competitive, single source requirements assuring contracts to existing Shuttle suppliers.”

“ In the summer of 2019, a former ULA employee claimed that Boeing, NASA's prime contractor for SLS, viewed orbital refueling technology as a threat to SLS and blocked further investment in it.”

“ In 2019, the Government Accountability Office found that NASA had awarded Boeing over US$200 million for service with ratings of good to excellent despite cost overruns and delays”

“ On 1 May 2020, NASA awarded a US$1.79 billion contract extension for the manufacture of 18 additional RS-25 engines. Ars Technica, in an article published on the same day, highlighted that over the entire RS-25 contract the price of each engine works out to US$146 million, and that the total price for the four expendable engines used in each SLS launch will be more than US$580 million. They critically commented that for the cost of just one engine, six more powerful RD-180 engines could be purchased, or nearly an entire Falcon Heavy launch with two thirds of the SLS lift capacity.”

https://en.m.wikipedia.org/wiki/Space_Launch_System

http://www.competitivespace.org/issues/the-senate-launch-sys...